Adolescence is a critical period for smoking initiation and progression. Of adults ever smoking regularly, the majority initiated smoking during adolescence and progressed to a regular habit by age 18. Thus, there is a pressing need to identify factors that protect adolescents from initiating smoking and progressing to a regular habit. One possibility is antismoking parenting. Parenting practices such as forbidding smoking indoors have been shown to reduce the likelihood of adolescent smoking. Although antismoking parenting appears protective, it is unclear whether all practices protect equally, and why. Given that alternative rewarding activities (e.g., team sport), anti-tobacco industry attitudes, smoking-related beliefs (e.g., perceived adult disapproval of smoking), stereotypes (e.g., smokers are stylish) and judgment (e.g., "I don't mind it if my friends smoke") of youth smokers, and peer smoking are related to positive parenting, antismoking parenting and adolescent smoking, they are potential mechanisms (mediators) to explain the relationship between antismoking parenting and adolescent smoking. That is, the effect of antismoking parenting on adolescent smoking may result in part from its indirect effects through one or all these possible mediators. It is also unclear whether antismoking parenting practices benefit equally those adolescents living in smoking and non-smoking households. The proposed study will fill these research gaps by examining direct, indirect, and moderated relationships between a range of antismoking parenting practices and adolescent smoking progression in a cohort of 750 adolescents followed from 9th (age 14) to 10th grade (age 15). A bioecological approach provides the theoretical framework for this research, as it emphasizes the effect of proximal processes (e.g., antismoking parenting) within the face-to-face setting (e.g., household) on developmental outcomes (e.g., smoking). The proposed study will evaluate the overall effect of antismoking parenting on adolescent smoking, the indirect effect through potential mediating mechanisms, and whether any one practice is most protective. Further, latent growth curve modeling (LGCM) will permit accounting for both inter and intra-individual variation in smoking behavior across time. Finally, the proposed study will evaluate whether the protective effect of antismoking parenting differs depending on whether adolescents live with family members who smoke. This will be the first study to test these relationships in a single model, and the first to assess the effects of antismoking parenting on adolescent smoking from a bioecological framework. Such unique data will be critical to developing efficacious youth smoking prevention and intervention programs. The ultimate goal of this tobacco control research is to understand how antismoking parenting practices affect adolescent smoking progression, evaluating the relationship between the amount of antismoking parenting practices and smoking progression, identifying the mechanisms of effect, and evaluating who benefits most from antismoking parenting. This will be the first study to test these relationships, and the first to assess the effects of antismoking parenting on adolescent smoking in a bioecological framework. Such unique data will be critical to developing effective youth smoking prevention and intervention programs.